Known vehicle brake fluid pressure control devices that perform ABS control include pressure increase control valves disposed in brake conduits that connect a master cylinder (hereinafter “M/C”) to wheel cylinders (hereinafter “W/C”) provided in each wheel. The pressure increase control valves control the flow of brake fluid to each W/C, and are normally open solenoid valves that can be controlled to two-positions, namely, an open position and a closed position.
When a pressure increase mode is set during ABS control of a vehicle brake fluid pressure control device like that described above, the pressure increase control valve is opened for determined periods to apply the M/C pressure to the W/Cs. However, because the pressure increase control valve is rapidly switched between open and closed positions, namely, because pulsed pressure increase is performed as is standard in known technology, a pulsing sound (operating noise) is generated every time switching takes place. To address this problem, technologies have been proposed (for example, in Japanese Patent Application Publication No. JP-A-2003-19952) in which the pressure increase control valves are controlled like a linear valve by adjusting the control current (the amount of current) to the pressure increase control valves (this control will be referred to hereinafter as “linear operation” or “operated linearly” depending on the context). Use of this configuration allows the pulsing sound that occurs in the pressure increase mode to be reduced.
More specifically, in each pressure increase control valve, the pressure differential between the upstream and downstream sides is changed in accordance with the size of the gap between the valve element and the valve seat inside the valve. Accordingly, if the magnitude of the control current is changed to adjust the size of the gap, namely, to adjust the pressure differential between the upstream and downstream sides of the pressure increase control valve, linear operation of the pressure increase control valve can be achieved. Thus, the pressure increase control valve does not rapidly switch between open and closed positions, whereby pulsing noise is reduced (as in the example of Japanese Patent Application Publication No. JP-A-2003-19952).
If the W/C pressure is smoothly adjusted by performing linear operation of the pressure increase control valve as in the art described above, the relationship of the control current applied to the pressure increase control valves and the pressure differential is extremely important. However, this relationship is liable to change if there is variation in the characteristics of the pressure increase control valves caused by manufacturing error. In this case, the adjustment accuracy of the W/C pressure falls.
To address this difficulty, a known art (refer to Japanese Patent Application Publication No. JP-A-H11-147466) proposes a configuration for brake fluid pressure control in which a brake ECU directly measures the characteristics of linear valves (solenoid valves). The characteristics are then stored in the brake ECU, and operation performed in accordance with the characteristics of the linear valves (solenoid valves). Accordingly, a fall in adjustment accuracy due to variation in the characteristics of the linear valves (solenoid valves) is inhibited.
However, if the characteristics of the solenoid valves are directly measured in this way, a device for measuring the characteristics must be provided in the brake ECU, which makes the vehicle brake fluid pressure control device more complicated and more expensive. In order to avoid these problems, the characteristic measuring device could be omitted by (i) trying to reduce the variation in the characteristics of the solenoid valves caused by manufacturing error, or (ii) measuring the characteristics of the solenoid valves first and then only selecting good solenoid valves for use in the vehicle brake fluid pressure control device. However, if the former approach were used, the manufacturing costs of the solenoid valves would be increased by the need for more rigorous management of the design and processing of the solenoid valves. On the other hand, if the latter approach were used, the manufacturing yield would reduce because the un-suitable solenoid valves that were not selected would have to be done away with.